OTTAWA - A visibly weak Chief Theresa Spence made a brief appearance on Sunday — in Day 20 of her fast —as a parade of politicians and protesters turned up the volume to demand action from the Harper government on treaty issues.

Through a spokesperson, the chief of the Attawapiskat First Nation said she was "deeply humbled" by the support she's received from aboriginals and non-aboriginals in her appeal for a face-to-face meeting with Prime Minister Stephen Harper and Gov. Gen. David Johnston.

A demonstration in support of her hunger fast took place at Toronto's Eaton Centre, where protesters crowded a section of the mall in a loud, but peaceful gathering.

There were also demonstrations at the legislature in Edmonton and in Calgary, outside of Harper's constituency office.

The main rail line between Montreal and Toronto was blocked for several hours Sunday evening delaying Via Rail passenger trains but traffic was moving later in the evening.

Spence acknowledged the outpouring from members of the Idle No More movement, but called for other First Nations leaders to also step up.

"This is a call to arms and a call to action in the most peaceful and respective way that reflects our natural laws as Indigenous nations," she said in the statement. "First Nations leadership need to take charge and control of the situation on behalf of the grassroots movement. We need to re-ignite that nation-to-nation relationship based on our inherent and constitutionally protected rights as a sovereign nation. We are demanding our rightful place back, here in our homelands, that we all call Canada."

Spence invited MPs and senators to visit over a two-hour period Sunday at her teepee, situated on an island in the frozen Ottawa River looking up at Parliament Hill.

Former prime minister Joe Clark, the highest-profile visitor, made an appearance Saturday, meeting with Spence and issuing a statement that said honest conversation can often lead to common ground.

Members of both the opposition NDP and Liberals expressed concern Sunday for Spence's health.

"She's a very determined woman and she's heard the message from others that she's done what people think she needed to do, but she noted that the prime minister has not talked to anyone, or put out a message that he is willing to meet with leaders, and that's all she's asking for," said New Democrat MP Paul Dewar, who was among 16 of the party's politicians to be invited inside.

Both Dewar and fellow New Democrat Craig Scott said they were worried about her condition.

"She's very peaceful in her demeanour, but that goes along with being quite weak now," said Scott. "She talks about sleeping more than she had earlier, in the first two weeks. I think it's very clear it's starting to take a physical toll."

Concern is strong enough that some have urged her to give up and let Opposition politicians take up the fight — something Craig said he tried to convey to her.

"I spoke directly to her and said, 'You know, you've done more anybody could expect one person to do, and there's no reason you and you alone should have to carry this burden.' And she said, 'It's my burden to carry.'"

Spence stopped eating solid food on Dec. 11.

An adviser to the chief and band council said there is no backing down.

"The chief is a strong-spirited, determined individual," said Danny Metatawabin. "We need to get the message out to the prime minister of Canada.

"Although she is drinking her liquids of water and fish broth, you know, she is getting weak in body when you don't eat solids. The body tends to shut down. They should just come and talk to us. Why are we afraid to communicate with one another?"

Health Minister Leona Aglukkaq joined other federal officials Friday asking Spence to accept a meeting with Aboriginal Affairs Minister John Duncan, but Spence rejected the recommendation.

The government points to a meeting it held last January with First Nations leaders as proof it is serious about improving their relationship, and adds it has spent millions on aboriginal health, housing and education.

But aboriginal leaders say they are being left out of the discussion the Harper government is having about how best to develop Canada's lucrative natural resources.

Joe Clark, who was a Tory prime minister from 1979 to 1980, said friends of his in the First Nations community had suggested he meet with Spence, chief of a remote reserve in Northern Ontario.

"My experience has been that direct and honest dialogue is always useful and sometimes essential, particularly in dealing with issues as complex and multi-faceted as the relations between First Nations and Canada," he said in a statement.

"Chief Spence expressed a humble and achievable vision — one which I believe all Canadians can embrace."